I have had this happen also. It is probably caused by engraving on one side of the acrylic, expanding that side of the material just slightly because it has been heated. The other side of the material has not been heated therefore did not expand. If you take a piece of acrylic, say about 1" wide and 10" long, place it on a towel, heat one side with a hair dryer, you will see the acrylic start to warp. My guess is the same thing is happening, but since the engrave is permanent, it stays warped.
It is possible that is your main cause judging from the design. The acrylic can handle it, but the heat from such detail is causing it. You could do the painstaking task of breaking the design apart in a few different colors so each area has time to cool, but I would suspect with that detail you would still have some warping.
As Goobdoob said, breaking up the file so the laser doesn’t dawdle in any one place may help.
As for fixing the warp you can try placing it on a baking sheet and putting it at a low temp in the oven. Google acrylic slump bowls, or heat forming acrylic and you’ll see how to warp acrylic into a bowl. In this case you want to do the reverse, but I would think it should work. The question is will it blur the engraves and does it work with mirrored acrylic (as opposed to non-mirrored acrylic.) I’d let @jamesdhatch weigh in with his opinion. He does a lot of slump bowls.
Ill give that ago thanks. Also its interesting as I have done this design on clear, black and normal gold acrylic no problem so maybe mirror acrylic its particular prone to it.
My wife has explicitly stated nothing in the oven that is NOT food. (shrug).
First time I had an issue like this, the oven was what I was going to try, but that got vetoed.
I used a low torch and quickly passed it over the design with the raised edge up and a light weight on it until it was flat.
If you use a torch the key is the spacing and waving over the area. Torches are used for heating vinyl used on car wraps too. The materials have a “memory” and will want to revert to their original flat appearance if you give them heat.
If you have a good heat gun (not a hair dryer) it will achieve the same thing as a torch. It however needs to be used the same way as it too can scorch the material.
I don’t know how your wife would feel about this, but I used our grill outside on the deck. Still an enclosed heated environment, but I felt better about it than using my oven in the house.
Having had my own “craft kitchen” for the past 8 months, I can’t tell you how amazingly nice it is to have the sink, appliances, and countertops, not to mention cabinet space, available for crafting purposes!
Note to self: Add “second living area” to the list of requirements for our next house.
As others have said, reheat it (annealing - removes internal stresses). Get a flat glass (tempered) cutting board and place your acrylic piece on it in the oven. Then heat the oven to 180F and leave it for an hour (technically full annealing takes 1hr/mm but an hour gets you 90% of the benefit).
If you’re not allowed to use the kitchen oven a gas grill works very well. Just dial in the heat & you’re good to go.
BTW, you can use pyrex bowls (for slumping) or casserole dishes for flattening too - you don’t need a flat glass cutting board. Of course SWMBO may object to the use of her pyrex to do acrylic heat tricks
Just an update for anyone interested or reading this post in the future. I have not used the oven yet to remove the heat stress but I did however change from scoring with High Quality settings to Draft and that made a huge improvement.
